icengines-140301050002-phpapp02.pdf

M S Steve

Assistant professor

Dept of Mechanical Engineering

Amal Jyothi College of Engineering

1 [email protected]

Heat Engines

Absorb energy in the

form of heat

Convert part of it into

work

Reject balance as heat

2 [email protected]

Combustion

3 [email protected]

Heat Engines

1. External Combustion Engines steam engine

2. Internal combustion Engines automobile engine

4 [email protected]

Internal Combustion Engine Burns fuel and air in enclosed space

Produces hot burned gases

Converts some of this heat into

useful work

Allows heat to flow from hot engine to cold outside air

Nikolaus Otto patented the 4-stroke engine when he was only 34!

5

[email protected]

Internal Combustion Engines are those

heat engines where the combustion of

the fuel takes place inside the engines

6 [email protected]

Advantages of I C Engines

1. High thermal efficiencies ( 30 to 35%)

2. Higher power to weight ratio

3. Compact and suitable for portable applications

4. Quick-starting and simple in construction

7 [email protected]

Disadvantages of I C Engines

1. Since fuel combustion occurs in the cylinder, consequent

very high temperatures of engines necessitates engine

cooling arrangements

2. High temperatures restrict ICEngines to be single-acting,

reducing the power strokes per revolution

8 [email protected]

Classification of IC Engines

According to:

Fuel used

Strokes per cycle

Thermodynamic cycle

Speed of engine

Method of ignition

Method of cooling

Method of governing

Arrangement of engine cylinders

Number of cylinders

Application

9 [email protected]

Arrangement of Cylinders

10

Arrangement of Cylinders

11 [email protected]

Comparison of Petrol and Diesel Engines

PETROL ENGINE

1. Works on Otto Cycle

2. Fuel-air mixture is admitted during suction stroke

3. Spark ignition

4. Low compression ratios (6 to 10)

5. Lower engine efficiency

6. Higher fuel consumption

7. Lower engine vibrations and noise

8. High running cost

9. Light duty application

DIESEL ENGINE

1. Works on Diesel Cycle

2. Fuel is injected at the end of compression stroke

3. Compression ignition

4. High compression ratios (10 to 20)

5. Higher engine efficiency

6. Lower fuel consumption

7. Higher engine vibrations and noise

8. Low running cost

9. Heavy duty application


IC Engine


IC Engine Parts

1. Cylinder Head

2. Cylinder Block and Liner

3. Piston

4. Connecting Rod

5. Crankshaft

6. Crank Case and Sump


Cylinder head


Engine valves


Valve mechanism


Piston assembly


Crank case


Crank shaft assembly


Four Stroke and Two Stroke Engines


Four Stroke I C Engine

In a four stroke I C Engine, one cycle of operation is

completed in four strokes of the piston in the engine

cylinder

The strokes are:

1. Suction (Induction) stroke

2. Compression Stroke

3. Power Stroke

4. Exhaust Stroke


Suction (Induction) stroke


Compression Stroke


Power Stroke

26

Exhaust Stroke

27

Spark plug

Inlet valve

Exhaust valve

Cylinder

Piston

The four-stroke engine


Inlet valve

open

INDUCTION STROKE



Inlet valve

open

Piston down INDUCTION STROKE



Inlet valve

open



Charge in


Inlet valve

open

Charge in


INDUCTION STROKE


Inlet valve

closed

COMPRESSION STROKE


Piston up

Exhaust valve

closed


Inlet valve

closed

POWER STROKE


BANG

Exhaust valve

closed


Inlet valve

closed

POWER STROKE


Piston down

powerfully

Exhaust valve

closed


Inlet valve

closed

POWER STROKE


Exhaust valve

closed


Inlet valve

closed

EXHAUST STROKE


Exhaust valve

open


Inlet valve

closed

EXHAUST STROKE


Exhaust valve

open

Piston up

Exhaust gases

out


Inlet valve

open

INDUCTION STROKE


Exhaust valve

closed


And so the

cycle

continues!!


1. Induction Stroke Engine pulls piston out of cylinder

Low pressure inside cylinder

Atmospheric pressure pushes fuel and air mixture into cylinder

Engine does work on the gases during this stroke


Engine Stroke 1

Fuel and air mixture after induction stroke: Pressure = Atmospheric

Temperature = Ambient


2. Compression Stroke Engine pushes piston into

cylinder

Mixture is compressed to high pressure and temperature



Engine Stroke 2

Fuel and air mixture after compression stroke:

Pressure = High

Temperature = Hot


3. Power Stroke

Mixture burns to form hot gases

Gases push piston out of cylinder

Gases expand to lower pressure and temperature

Gases do work on engine during this stroke


Engine Stroke 3

Burned gases after ignition: Pressure = Very high

Temperature = Very hot


Engine Stroke 4

Burned gases after power stroke: Pressure = Moderate

Temperature = High


4. Exhaust Stroke

Engine pushes piston into cylinder

High pressure inside cylinder

Pressure pushes burned gases out of cylinder



Two Stroke Engines

55

[email protected]

Two Stroke I C Engine

In a two stroke I C Engine one cycle of operation is

completed in two strokes of the piston in the engine cylinder

Stroke 1: Scavenging and Compression

Stroke 2: Power and Exhaust


Scavenging and Compression

59

[email protected]

Power and Exhaust

60

Advantages of Two Stroke engines

1. One power stroke every revolution of crankshaft results in high power to weight ratio

2. Torque is more uniform needing lighter flywheel

3. Simpler in construction due to absence of valves and valve gear

4. Friction loss is less giving higher mechanical efficiency

5. Lower initial cost

6. Easier starting


Disadvantages of Two Stroke engines

1. Overall efficiency is less due to:

a) Inadequate scavenging as some combustion products remain in cylinder

b) Loss of fresh charge during scavenging

c) Less effective compression ratio for same stroke length

2. Engine overheating due to power stroke in every revolution

3. High lubricating oil consumption

4. Exhaust is noisier


Comparison of Four Stroke and Two Stroke Engines

FOUR STROKE ENGINE

1. One cycle in 4 strokes of piston or 2 revolutions of crankshaft

2. Valves are used for charge admission and exhaust

3. One power stroke in two revolution causing torque fluctuations needing heavy flywheel

4. Low power to weight ratios

5. Higher overall efficiency

6. Complex construction due to valve gear

7. Heavy duty applications

TWO STROKE ENGINE

1. One cycle in 2 strokes of piston or one revolution of crankshaft

2. No valves but ports are used for admission and exhaust

3. One power stroke in one revolution causing smoother torque and consequent lighter flywheel

4. Higher power to weight ratios

5. Lower overall efficiency due to loss of fresh charge

6. Simpler construction

7. Light duty applications


I C Engine Systems 65

I C Engine Systems

1. Air & Exhaust System

2. Fuel Systems

3. Ignition Systems

4. Cooling Systems

5. Lubrication Systems


AIR SYSTEM FOR PETROL

ENGINE


AIR SYSTEM FOR PETROL ENGINE

AIR FROM ATM

SILENCER Product of combustion to atm

Engine AIR FILTER Carburettor


FUEL SYSTEMS

Petrol Engines

Diesel Engines


Fuel Systems

Petrol Engines

Correct quantity of petrol is mixed with air in carburettor before

being admitted into cylinder during suction stroke


Fuel storage tank

Fuel Pump Fuel Filter Carburettor Engine

FUEL SYSTEM FOR PETROL ENGINE

AIR FROM ATM AIR FILTER

combu

stion


FUEL SYSTEM FOR PETROL

ENGINE


FUEL SYSTEM FOR DIESEL ENGINE

AIR FROM ATM

SILENCER Product of combustion to atm

Engine

Low

pressure

pump

AIR FILTER

Fuel storage tank

filter filter High

pressure

pump

Fuel Injector


FUEL PUMP

74

It pumps fuel from storage tank to carburetor

Actuated by cam, it is in touch with rocker arm

As the link is pulled downwards diaphragm will move down

and fuel will enter the chamber

Inlet and Exhaust valves are one way valves


One-way

Inlet Valve

One-way

Outlet Valve

Diaphragm

Driving Cam

Diaphragm Pump 76

Air

Filter

Tank

PETROL ENGINE Carburettor Fuel System

Cockpit

Gauge

Pump

Carburettor

Exhaust Inlet

77

SIMPLE CARBURETOR WORKING

FLOAT CHAMBER

FLOAT NEEDLE VALVE AIR VENT VENTURI

FUEL

FEED @

PUMP

JET

FLOAT

FUEL

LEVEL


Major function of carburetor is to provide air fuel mixture

Basic principle : When a volatile fuel is placed in the passage

of high velocity air, the fuel gets vaporized at a faster rate

Arrangement: Jet and fuel nozzle

Venturi tube & venturi throat

Float chamber

Throttle valve

Float , float needle, air vent


Working

1. Petrol is pumped into the float chamber, level of petrol is

maintained by a float arrangement

2. Suction stroke of engine causes air flow through venturi tube.

3. VELOCITY of air at throat will increase & PRESSURE will decrease at JET point(will be less than Atm. Pressure)

4. In float chamber the pressure acting is Atm. Pressure, due to this

pressure difference fuel will flow from FLOAT CHAMBER to

the JET

5. Function of throttle is to control speed and power to engine,

more the throttle is closed flow of air & fuel mixture to the

cylinder is less


AIR IS SUCKED THROUGH VENTURI ..

A PISTON MOVING DOWN ON SUCTION STROKE


MOVING AIR HAS LOWER PRESSURE

FUEL

FLOW AIR

FL

OW

AIR

FL

OW

THE LOWER AIR PRESSURE PULLS FUEL THROUGH THE JET

AIR/FUEL

MIXTURE

FLOWS TO

ENGINE

FUEL LEVEL DROPS

83

[email protected]

PULLING AIR INTO FLOAT CHAMBER


FUEL LEVEL DROPS

FUEL LEVEL DROPPING LOWERS FLOAT

84

AND ALLOWS FUEL TO ENTER FLOAT CHAMBER FROM PUMP


FUEL LEVEL DROPS

FUEL LEVEL RISING FORCES THE NEEDLE VALVE CLOSED

FUEL LEVEL DROPPING LOWERS FLOAT

85


FUEL IS PULLED OUT OF THE FLOAT CHAMBER

ONLY WHEN PISTON IS ON THE INDUCTION STROKE

FUEL LEVEL RISING FORCES THE NEEDLE VALVE CLOSED

86

We now need to look at controlling

the air/fuel mixture flowing into the

engine

Controlling the air/fuel mixture

means controlling the engine

The carburettor part which controls

the flow is.

THE THROTTLE


THROTTLE

VALVE

SIMPLE CARBURETOR WORKING 88

THROTTLE VALVE

THIS WOULD BE A HIGH THROTTLE SETTING OR FULL POWER

OPEN THROTTLE ALLOWS VENTURI TO WORK AT MAXIMUM EFFICIENCY


LOW THROTTLE SETTING - CALLED IDLE OR TICK-OVER

ALMOST CLOSED THROTTLE MEANS THE VENTURI DOES NOT WORK VERY

WELL

LOW AIR FLOW MEANS VERY LITTLE OR NO FUEL/AIR MIXING IN THE

VENTURI

SO AN ALTERNATIVE AND EFFECTIVE VENTURI NEEDS TO BE FOUND


T CONTROLS FUEL FLOW

LOW THROTTLE SETTING - CALLED IDLE OR TICK-OVER

EDGE GAPS BECOME THE VENTURI FOR THE LOW AIR FLOW

AT IDLE - SLOW RUNNING JET


LIMITATIONS OF CARBURETTOR

Distribution of air /fuel mixture to cylinder is not uniform

Construction of venturi causes low volumetric efficiency

There is a loss of volumetric efficiency also due to restricted flow of mixture in various parts such as chokes, tubes, jets,

throttle valve, inlet pipe bends, etc.

All the above limitations of carburettor can be avoided by introducing the fuel

through injection rather than the carburettor

93

FUEL INJECTION PUMP

A fuel injection pump is used to supply precisely metered quantity of diesel under high pressure to the injectors at the correct time.


FUEL PUMP

Spring

Delivery valve

Fuel overflow port

Barrel

Rack

plunger

Inlet port


barrel

Barrel houses the inlet port and fuel overflow port

99

Plunger

Plunger driven by cam & tappet

Plunger reciprocates in a barrel & fuel enters thru inlet port

Plunger have a vertical and helical groove which help in determining the amount of fuel supplied to the fuel injector


Delivery valve is a non return valve, kept in position by a spring.

When the Pr. In the barrel exceeds a

predetermined value and valve opens

against the compression of the spring

and the pressure of the fuel above.

Fuel pump is connected to the fuel

injector through a passage


Working

When the plunger is at bottom the fuel inlet & overflow

ports are uncovered and filtered fuel is forced into the barrel

Both ports are covered when the plunger moves upwards

Fuel will get compressed when the plunger moves further

forward

The high pressure lifts the delivery valve and fuel flows out

thru the delivery valve

With further rise of the plunger the overflow port is

uncovered by the plunger and pressure drops


The quantity of fuel pumped can be varied by the angular

position of the helical groove relative to the inlet port

103

Diesel Fuel Pump

Plunger reciprocates on a barrel(hollow cylinder like

arrangement)

A rectangular helical groove in the plunger which extends

from top to another helical groove

When the plunger is at bottom -- fuel inlet and overflow port

are open,--fuel will come inside the barrel

When the plunger moves up both ports are closed and fuel

inside the barrel get compressed

Due to the high pressure of compressed fuel delivery valve

will get opened


FUEL INJECTOR


FUEL INJECTOR

A fuel injector is used to inject the fuel in the cylinder in atomised form and in proper quantity. Fuel injectors are available in several designs. Main components of fuel injectors are : NOZZLE

VALVE BODY SPRING

The nozzle is its main part which is attached to the nozzle holder. Entry of fuel in the injector is from the fuel injection pump.


FUEL INJECTION NOZZLE


Spray Structure

110

PARTS OF FUEL INJECTOR

1. Nozzle valve

2. Nozzle body

3. Spring

4. spindle

5. Adjusting screw

6. Lock nut

7. Passage

8. Nozzle

9. Leak of connection

111

Nozzle valve is fitted in a nozzle body.

The spring retains the valve in its seating through a spindle.

Adjusting screw and lock nut- to adjust the lift of the nozzle


Working High pressure fuel from the fuel pump enters the injector

through the passage and lift the nozzle valve

Fuel travels down the nozzle and is injected into the engine

cylinder in the form of fine spray

When the fuel pressure drops the spring force overcomes the

fuel pressure and the valve get closed

Any leakage of the fuel at the end of the compression is fed

back to the fuel pump suction chamber by the leak off pipe


FUEL INJECTOR


Nozzle valve is held on its seat by a spring which exerts

pressure through a spindle

Fuel from fuel pump enters the passage and lifts the

nozzle valve

then the fuel will sprayed through the nozzle and is injected

into the engine

When pressure drops the nozzle valve will occupy in its

seat under the compression of the spring


Ignition Systems Ignition process in Petrol Engines requires an electric spark

produced at the spark plug.

This spark is generated by an electric discharge produced by the ignition system.

Ignition systems in petrol engines are classified as :

1.Battery ignition system.

2.Magneto ignition system

The difference between the two systems is in the source of primary voltage.


Ignition systems

Basic requirements of an ignition systems

A source of electrical energy

A device for boosting the low voltage to produce high voltage

A device for timing and distributing the high voltage to each

spark plug


Battery Ignition System.

118

Battery ignition system

It is also called coil ignition system.

The source of energy to the primary windings is a 6V or

12V battery.

As the number of windings in the secondary is 50 to 100

times more than that of the primary , the output voltage

induced will be of the order of 10000v to 20000V.


Magneto Ignition System

120

Magneto ignition system

The source of energy is either rotating magnets with fixed

coils or rotating coils with fixed magnets.

The rapid collapse and reversal of magnetic field induces a

very high voltage in the secondary winding.

It is generally employed in racing cars, motor cycles etc.


Spark plug

Task-

The spark plug ignite the suctioned and compressed fuel-air

mixture due to arcing between the electrodes.

Function-

The ignition voltage travels to the spark plug from directly

Connected ignition coils or over the ignition lines from the

Ignition coils causing arcing in the air gap between the center

and ground electrodes.


The Spark Plug

Centre electrode receives coil voltage.

Insulator prevents high voltages

from shorting to ground.

Terminal

Gap

Insulator

Gasket

Thread

Metal

shell

Hex

Centre

electrode

Side

electrode

Spark plug is located in the cylinder head,

it ignites the air and fuel mixture.

Has centre and side electrodes,

with an air gap between them.

High voltage jumps the

air gap, creating a spark.

Side electrode is grounded.

Next > 123

Lubricating Systems

Purpose:

1. To reduce friction and wear

2. To provide sealing between piston and cylinder

3. To cool piston heads, valves, etc.

4. To wash away carbon and metal particles


Lubrication Systems:

1. Petroil lubrication

2. Wet sump lubricating system

1. Splash lubrication

2. Pressure lubrication

3. Dry sump lubricating system


Petrol Lubrication System

This system of lubrication is used in scooters and motor

cycles.

About 3% to 6% of lubricating oil is added with petrol in the

petrol tank.

The petrol evaporates when the engine is working. The

lubricating oil is left behind in the form of mist.

The parts of the engine such as piston cylinder walls,

connecting rod are lubricated by being wetted with the oil

mist.


Wet sump lubrication system The splash system is used only on small four-stroke-cycle

engines.

As the engine is operating, dippers on the ends of the connecting rods enter the oil supply, pick up sufficient oil to lubricate the connecting-rod bearing, and splash oil to the upper parts of the engine.

The oil is thrown up as droplets, or fine spray, which lubricates the cylinder walls, piston pins and valve mechanism.

In the pressure-feed system, oil is forced by the oil pump through oil lines and drilled passageways.

The oil, passing through the drilled passageways under pressure, supplies the necessary lubrication for the crankshaft main bearings, the connecting-rod bearings piston-pin bushings, camshaft bearings, valve lifters, valve push rods, and rocker studs.


Splash lubrication

Simplest of all types, used only for small capacity engines.


Pressure lubrication

129

[email protected]

Dry Sump Lubrication System In a wet sump, the oil pump sucks oil from the bottom of the

oil pan through a tube, and then pumps it to the rest of the

engine.

In a dry sump, extra oil is stored in a tank outside the

engine rather than in the oil pan. There are at least two oil

pumps in a dry sump -- one pulls oil from the sump and

sends it to the tank, and the other takes oil from the tank and

sends it to lubricate the engine. The minimum amount of oil

possible remains in the engine.


Dry sump lubrication

The supply of oil is from an external tank.

An oil pump is employed to circulate the oil under pressure

,from the tank to various bearings of the engine.

131

Functions of a Lubricant Lubricant reduces friction between moving part.

It reduces wear and tear of the moving parts.

It minimizes power loss due to friction.

It provides cooling effect. While lubricating it also carries

some heat from the moving parts and delivers it to the

surroundings through the bottom of the engine (crank case).

It helps reduce noise created by the moving parts.


THE COOLING SYSTEM


Purpose of cooling

To regulate the engines internal temperature

To remove excess heat from the engine

To prevent heat to the passenger compartment

To Control temperature of hot combustion,4000 degree temps. could seriously damage engine parts.

Cool Trans fluid & Oil


Cooling Systems Intense heat is generated during the combustion of fuels

inside the engine cylinder.

30% of heat generated is converted into mechanical work & 40% is carried away by exhaust gases to the atmosphere.

The remaining part of heat (30%) will be absorbed by the engine parts which leads to overheating of these parts.

In order to avoid the problem of overheating it is essential to provide some kind cooling systems.


The two important characteristics of cooling systems for

the efficient working are:

(i)It should not remove more than 30% of heat

generated.(larger amount of heat removal reduces the

thermal efficiency)

(ii)The rate of cooling should not be constant.(the rate

of cooling should increase with increase in heat

generated)


Two types of cooling systems used in IC engines are:

1.Air cooling system

2.water cooling system


Air cooling

The heat is dissipated directly in to the atmospheric air

by conduction through cylinder walls.

The rate of cooling is increased by increasing the outer

surface area of the cylinder by providing radiating fins &

flanges.

Normally it is used for the engines of motor cycles ,

scooters etc.


To increase the surface area exposed fins are provided

In some cases blower is provided to increase the heat tr. rate


Air cooling system

140

Air cooling

Heat is dissipated to the surrounding air around the cylinder

Basic principle- to have continuous flow air around parts

which are to be cooled

The heat dissipated depends on :

The surface area of the metal, in contact with the air flow

The Temp difference between the surface & the air

Thermal Conductivity of the metal


Advantages of Air-cooled Engines:

Air-cooled engines are smaller and lighter because they dont

need to house any of those parts like the Water cooled engines

In some climates, water has the tendency to freeze and this is a

problem for water-cooled engines.

Air-cooled engines warm up quickly and are easy to maintain.

Disadvantages of Air-cooled engines:

The cooling tends to be uneven and leads to cylinder distortion.

It is almost impossible to manage with air-cooling if the number

of cylinders increases beyond two.

The fins vibrate sometimes leading to a lot of noise.


Water cooling system.

It is also called thermosyphon system of cooling .

Water is circulated through water jackets around each of the

combustion chambers.

The circulating water is cooled by the air drawn through

radiator by a fan


Liquid cooling (water cooling)

Cooling medium water

Water circulated through the passages

around the main components

Passages water jackets

Water circulation- pump or by gravity

force


Water after passing through the jackets flows to a radiator.

Radiator cools hot water with the help of moving air around the

radiator tubes

Fans are provided to increase the heat transfer rate

This system also uses a thermostat to control the flow of the

coolant

Antifreeze added to avoid freezing of coolant- ethylene glycol


Water cooling system


147

Water Jackets Surrounds the cylinders

with water passage.

Absorbs heat from the

cylinder wall.

Pump move water to

radiator where heat is

exchanged to the air.

[email protected]

148

Radiators

A radiator is a heat

exchanger.

Tube and fin style the

most popular.

Made of copper and

brass or aluminum and

plastic.

[email protected]

149

Its job is to block the flow of coolant to the radiator until the

engine has warmed up.

When the engine is cold, no coolant flows through the

engine. Once the engine reaches its operating temperature

(generally about 200 degrees F, 95 degrees C), the

thermostat opens.

By letting the engine warm up as quickly as possible, the

thermostat reduces engine wear, deposits and emissions.

[email protected]

INJECTION METHODS

150

TYPES OF CI INJECTION SYSTEMS

152

COMMON RAIL DIRECT INJECTION (CRDI)


COMMON RAIL

155

Working

HP fuel pump maintains fuel in the common rail at a pressure

of about 200 MPa.

Common rail branches off to ECU controlled injector valves

Valve contains precision machined nozzles and a plunger

driven by solenoid valves

ECU controls the timing and quantity of fuel injected

depending on the load conditions


Advantages of CRDI

Higher efficiency due to variable injection timing

Better combustion at low speeds

Better power balance- reduced vibration

Lesser moving parts

Compact engine


AIR FURL SYSTEM IN SI (PETROL)

ENGINES

159

Gasoline direct injection

Petrol Direct Injection or Direct Petrol

Injection or Spark Ignited Direct Injection

(SIDI) or Fuel Stratified Injection (FSI)


Components of GDI engine

Pumping element

Metering element

Mixing element

Mixture control

Distributing element

Ambient control


MULTI POINT FUEL INJECTION Petrol vehicles used carburettor for supplying the air fuel mixture in

correct ratio to cylinders in all rpm ranges.

Carburettor achieves this by breaking up fuel into minute particles and

mixing it with air.

But this process may not always be perfect and might reduce the

performance of the engine.

Therefore, multi point fuel injection system (MPFI) is used, which can

assure proper air fuel ratio to an SI engine.


MPFI

MPFI stands for multi-point fuel injection

It allows more efficient combustion of fuel, thereby

producing more power with less emissions

It is similar to CRDI in diesel engines

All modern petrol engines use MPFI systems


MULTIPOINT INJECTION

166

MPFI System

MPFI does the same function as the carburettor

It has injectors which spray correct quantity of fuel for each

cylinder

The fuel and air are mixed in the intake manifold before

admission to the cylinder


Components of MPFI

Electronic Control Unit (ECU)- sometimes called Engine

Control Module (ECM)

High Pressure Pump Module-pump, filter, pressure

regulator, common rail, sensor

Injector for each cylinder, also controlled by ECU


The function of ECU is to receive inputs from various sensors, compare them with pre-loaded engine and throttle parameters and send control signals to the actuators. Sensors: Sense different parameters (Temperature, Pressure, Engine Speed etc.) of the engine and send signal to ECU. Actuators: Receive control signal from ECU and actuates pump and injectors

ECU


Ambient temperature

Coolant temperature

Exhaust temperature

Exhaust oxygen content

Inlet manifold vacuum

Throttle position

ECU Inputs

Engine RPM

Vehicle road speed

Crankshaft position

Camshaft position

Outside air pressure

Pressure on throttle

For the Inputs, the microprocessor (or ECU) reads a number of

sensors:

Based on all these inputs from the sensors, the computer in the

MPFI system decides what amount of fuel to inject, when, for what

duration, and into which cylinder. It then sends signals to actuators

for injection of correct quantity of fuel.


Thus it makes the engine cleaner, more responsive, ensures

complete combustion, and uses less fuel as it knows what

amount of petrol should go in.

Modern cars ECUs have memory, which will remember

your driving style and will behave in a way so that you get the

desired power output from engine based on your driving

style.

For example, if you have a habit of speedy pick-up, cars

computer will remember that and will give you more power

at low engine speeds by putting extra petrol, so that you get a

good pick-up. It will typically judge this by the amount of

pressure you put on accelerator.


A multi-point injection system, also called port injection, has an

injector in the port (air-fuel passage) going to each cylinder.

Gasoline is sprayed into each intake port and toward each intake

valve. Thereby, the term multipoint (more than one location)

fuel injection is used.

175

Advantages of MPFI:

More uniform fuel-air mixture will be supplied to each cylinder.

Thus the power developed by different cylinders will be more

uniform.

More appropriate fuel-air mixture will be supplied, which will

increase the combustion efficiency.

Cold starting can be improved.

Immediate response in case of sudden acceleration and

deceleration.


ADVANTAGES OF MPFI SYSTEMS OVER

SPFI SYSTEM

MPFI SPFI

Better power Low power

Better refinement of engines Lesser refinement of engines

Better control over the process Lesser control over the process

Longer life due to lesser load per injector Lesser life due to higher load

Cleaning not required frequently Frequent cleaning is required

No delay in response Delay in response

No difference in delivery to each cylinder Difference in delivery to each cylinder

177

Thank you!!


icengines-140301050002-phpapp02.pdf

Documents

stroke engines

hot engine

engine valves

heat engines

diesel engines petrol

higher engine vibrations

higher engine efficiency

lower engine vibrations